Scrap tyre pyrolysis: Are the effluents valuable products?

Scrap tyre pyrolysis under nitrogen is studied at atmospheric pressure with the aim of producing a solid residue to be burned simultaneously with coal dust in a coal burning power plant. The experimental device maintains isothermal conditions. The temperatures of treatment are: 380, 450 and 550 degrees C. Three phases are obtained after pyrolysis: solid, liquid and gas and their composition is studied in relation to the temperature of the thermal treatment. The solid phase (char)-approximately 40% weight of the initial sample (steel free) mostly constituted of carbon, also contains the main mineral matter initially present in the used tyre. The char produced is brittle and has a high burning power which makes it suitable for burning when mixed with coal dust in coal burning power plants. The steel weave is easily separated from the solid carbon residue after the thermal treatment and recovered without physical or chemical change and can be recycled. The gas phase contains a mixture of light hydrocarbons, dihydrogen and carbon dioxide. The IRTF spectra of evolved gases shows a change in the ratio of every gas while the pyrolysis takes place. The liquid phase is a complex hydrocarbon mixture in which some components have been identified. The chemical-valorization of the liquid phase is an alternative to a thermal valorization. The pyrolysis appears to be a technique which is able to reduce a bulky, high polluting industrial waste, while producing energy and/or valuable chemical compounds. (C) 1997 Elsevier Science B.V.